Our objective is to attain an understanding of how epidermal keratinocyte growth and differentiation is regulated. Studies of epidermis taken from human subjects with skin disease can suggest areas of research on the control of epidermal cell function. In the skin disease psoriasis the epidermis is hyperproliferative, shows abnormal differentiation, and altered arachidonic acid and eicosanoid metabolism. Arachidonate is bound to cell membrane phospholipids. Two enzymes, phospholipase A2 and C, act on the phospholipids to release free arachidonate which is further transformed into an number of eicosanoids. 1,2 diacylglyceride (DAG), which is formed via the phospholipase C pathway, is biologically active; the cellular content of DAG may be controlled by DAG lipase activity. The available data allow the postulates that 1) the activity of phospholipase A2 and C, and of 1,2, DAG lipase are abnormal in psoriatic epidermis. 2) that the activity of these three enzymes and the cellular content of 1,2, DAG can control epidermal growth and differentiation. To test these hypotheses it is proposed 1) to determine the activity of phospholipase A2 and C, and of 1,2 DAG lipase in normal, uninvolved and lesional psoriasis, 2) To determine the activity of phospholipase A2, of phospholipase C, and of 1,2,DAG lipase in neonatal mouse keratinocyte cultures whose proliferative rate and keratin synthesis are altered by growth in a number of epidermal growth regulators. These are the glucocorticoids, desoximetasone and triamcinolone acetonide; two vitamin A analogues; cholera toxin and 8-BrcAMP, which augment cellular cAMP activity; the mitogen and tumor promoter TPA (tetradecanoy 1phorobol acetate); low calcium growth medium. Human epidermal biopsies will be assayed, and the functional studies will be done using primary neonatal mouse keratinocyte cultures. In vitro enzyme assays, thin layer chromatograph, high performandce liquid chromatography and radioimmune assays will be done. In continuing studies, monoclonal antibodies to keratin proteins will be used to study the keratin differentiation process. The studies will determine how arachidonic acid metabolism via two different pathways are involved in epidermal keratinocyte function.